Tweak sv_pos_b2u_flags check in pp_index

There's no need to run sv_pos_b2u_flags if the retval is one as
one byte can only be one character, therefore change the test to
"> 1". This makes index on unicode strings that match at 1 slightly
faster.

3 files changed, 12 insertions, 2 deletions

diff --git a/pp.c b/pp.c
index 49798e2d93..97ad595119 100644
--- a/pp.c
+++ b/pp.c
@@ -3343,7 +3343,7 @@ PP(pp_index)
 	retval = -1;
     else {
 	retval = little_p - big_p;
-	if (retval > 0 && big_utf8)
+	if (retval > 1 && big_utf8)
 	    retval = sv_pos_b2u_flags(big, retval, SV_CONST_RETURN);
     }
     SvREFCNT_dec(temp);
diff --git a/t/op/index.t b/t/op/index.t
index fd5a98fc48..29a477146e 100644
--- a/t/op/index.t
+++ b/t/op/index.t
@@ -8,7 +8,7 @@ BEGIN {
 }
 
 use strict;
-plan( tests => 121 );
+plan( tests => 122 );
 
 run_tests() unless caller;
 
@@ -253,3 +253,7 @@ is index('the main road', __PACKAGE__), 4,
     '[perl #119169] __PACKAGE__ as 2nd argument';
 
 } # end of sub run_tests
+
+utf8::upgrade my $substr = "\x{a3}a";
+
+is index($substr, 'a'), 1, 'index reply reflects characters not octets';
diff --git a/t/perf/benchmarks b/t/perf/benchmarks
index c137d0c9ec..52e2af9400 100644
--- a/t/perf/benchmarks
+++ b/t/perf/benchmarks
@@ -69,5 +69,11 @@
         setup   => 'my ($x, $y)',
         code    => '($x, $y) = (1, 2)',
     },
+
+    'expr::index::utf8_postion_1' => {
+        desc    => 'index of a utf8 string, matching at position 1',
+        setup   => 'utf8::upgrade my $x = "abc"',
+        code    => 'index $x, "b"',
+    },
 ];